New research published in The Proceeding of the Royal Society - Biological Sciences provides new insights on the threat ocean warming poses on coral growth in Mesoamerican barrier reefs. The research, partially funded by CPO's Climate Monitoring program, used laboratory experiments to examine the adverse effects of ocean warming and acidification, and showed that the warming predicted by the IPCC for the end of the 21st century produced a five-fold decrease in coral calcification - the process by which corals produce calcium carbonate (CaCO3) and build reefs.
“The reef-building coral Siderastrea siderea exhibits parabolic responses to ocean acidification and warming,” is part of on-going work of NOAA-funded researcher Dr. Justin Ries that is looking at various aspects of climate variability, change, and ocean acidification on coral growth. Dr. Ries and colleagues have been examining long term coral reef growth patterns at one of the largest barrier reefs in the world, off the coast of southern Belize. The research aims to create100 year records of coral growth at this reef by examining growth rates and environmental factors. As part of this work, Dr. Ries and his team found substantially decreasing growth rates over the last several years, at the same time that ocean acidification and temperature have been increasing.
This new research, led by post-doctoral researcher Dr. Karl Castillo, was designed to isolate the effects increasing ocean acidification and temperature had on Siderastrea sidereal, an important keystone and reef building coral species at the reef. By extracting coral colonies and returning them to the lab, researchers were able to design separate experiments around increasing temperature and decreasing ocean pH, and measure the coral response. While the most adverse effects on corals may arise from both acidification and temperature warming, researchers wanted to better understand the specific responses to these individually, which could aid efforts to predict and potentially mitigate the impacts of changing ocean conditions on coral.
They found that both ocean acidification and ocean warming had a “parabolic effect” on this important coral species. This means that while moderate decreases in the pH of seawater and moderate rises in temperature led to increases in coral building, in both cases researchers found a “tipping point” at which the coral calcification rates started decreasing. For ocean acidification, researchers recreated seawater conditions that would occur from the atmospheric carbon dioxide concentration from pre-industrial up through the present, the predicted end-of-century value, and up to six times the present condition. They found the “tipping point” at which calcification started leveling off and finally decreasing was actually well past the acidifications that would be expected by the end of century. For this particular species, they concluded, ocean acidification expected over the next century alone may not have a significant adverse effect.
For warming ocean temperatures, however, the results were very different. For the temperature experiments, researchers grew the coral colonies in temperatures from 25C to 32C, which covers the range of annual minimum and maximum temperatures of ocean temperatures recorded near the reef over 2002-2014, as well as annual average seawater temperatures expected over the next century. Thus the researchers were hoping to capture how the coral responds to the year to year variability seen now as well as what general conditions are predicted to by like by the end of the century. They found that while reef-building calcification rates increased for corals at 28C relative to 32C, skeletal building dropped off dramatically – nearly 80% - in corals growing at 32C. This parabolic response indicates that for this important reef building species, ocean warming over the next few decades could be an immediate serious threat, as conditions pass what the research found to be a species tipping point. Researchers note that the actual reef will experience changes in both stressors – ocean acidification and ocean warming – together over the next century, and will continue to work to understand how this and other reefs may respond.
You can watch a YouTube video on this and other aspects of Dr. Ries coral reef research here: https://www.youtube.com/watch?v=nvy7hFhiMZU
For the full open access journal article: http://rspb.royalsocietypublishing.org/content/281/1797/20141856.full
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